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The Derry Township Municipal Authority (DTMA) is an operating Authority whose service area includes the area in and around the unincorporated Village of Hershey, Pennsylvania. The DTMA is responsible for the collection, conveyance and treatment of wastewaters generated in Derry, South Hanover, Conewago, Londonderry, and Lower Swatara Townships. The collection system consists of approximately 150 miles of sanitary sewer, nine pumping stations and two wastewater treatment facilities (WWTF). The two WWTFs are the Southwest, an unmanned and fully automated 0.6 MGD satellite facility, and the Clearwater Road (CwR), a 5.0 MGD advanced secondary facility which includes the sludge treatment facilities for both treatment plants.

The Clearwater Road (CwR) WWTF treats wastewater from a service area with a population of approximately 18,000 people, numerous commercial and retail establishments, an amusement park, and pretreated effluent from the Hershey Chocolate Company Industrial Pretreatment Facility (IPF). In addition, the Clearwater Road WWTF also receives the industrial sludge from the IPF as well as significant volumes of septage from a hauled wastewater (septage) receiving program.

In 1998, as part of the planning and evaluation for a facilities improvements project at its CwR WWTF, the DTMA reviewed the solids treatment and disposal operations. At the time of the evaluation, the existing processes utilized at the CwR WWTF included raw wastewater pumping, primary clarification, complete mix activated sludge, ferric addition for phosphorous removal, final clarification, and UV disinfection. Primary, waste activated and industrial pretreatment sludge were thickened, blended, belt filter press dewatered, and stabilized using lime post treatment to create biosolids suitable for land application. Landfilling of biosolids cake was utilized when land application was unavailable. The approximately 40,000 gallons per day of septage received is lime stabilized prior to being discharged to the main plant treatment process flow stream.

The CwR WWTF produces more than 6 dry tons per day, significantly larger volumes of sludge than a typical 5.0 MGD WWTF. The primary clarifier sludge which includes 12 to 15 % additional lime stabilized solids from the septage receiving program, is gravity thickened. The waste activated sludge is air floatation thickened. The undigested, thickened, anaerobic pretreatment sludge is received directly from the IPF. Finally, a small, but volatile scum and grease component is removed from the various scum pits, the bulk of this material originates from the grease trap discharges to the septage receiving station.

Document Type: Research Article


Publication date: January 1, 2003

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